As foams of polymer compounds, foams produced using a thermoplastic resin such as polystyrene, polyethylene, polypropylene or polyvinyl chloride have been utilized in the form of beads, sheets, or boards, in the civil engineering and construction field, packaging field, electric appliance field, automobile field and the like, taking advantages of their characteristics such as thermal insulation properties, light-weight properties, and shock-absorbing properties. Any of these requires a facility on a large scale for providing their molded products. Additionally, these are often hard foams, in general.
Furthermore, as foams produced using a thermosetting resin by curing and expanding a liquid resin composition, polyurethane foams have been well known. The polyurethane foams can be molded simply with a facility on a small scale, and soft foams can be also produced (Patent Document 1). In addition, both hard and soft foams can comprise polyurethane, which achieves superior formability, and one type of such foams has been known as a low-resilience foam (for example, Patent Document 2). Moreover, for example, polyurethane foams being soft and having a high expansion rate also exhibit comfortable feel in wearing, and have been used by providing in garments as a protector (soft pad) for the purpose of preventing occurrence of wounds, and impacts against the body during playing sports.
However, they are disadvantageous in that isocyanate about which toxicity is concerned must be used. Furthermore, when a great impact load is imparted particularly, for example, such as in the event of a fall, a so-called “bottomed” state may be inevitable, whereby a problem of failing to sufficiently absorbing the impact can be caused. On the other hand, a hard pad is also used for the same purpose, but problems of inferior breathability and bad feel in wearing may be caused, although superior shock absorbing capacity can be achieved. Accordingly, a foam produced without using a material about which toxicity is concerned, which can be easily molded, and which is flexible and exhibits a favorable tactile impression has been demanded.
Low-resilience foams, generally referred to, reportedly have resilient modulus being no greater than 15 to 20%, in general. However, according to the measurement of the resilient modulus, the intensity of bound can be determined, but the slowness of the recovery of the sample cannot be evaluated. It is believed that when a person touches a sample, in a strict sense, not one having low resilient modulus, but one achieving retarded recovery with respect to the deformation is recognized as exhibiting low resilience. However, any procedure for evaluating the slowness of the recovery has not been found so far.
Foams comprising a silicone based polymer are disclosed in, for example, Patent Documents 3 to 5. Patent Document 2 discloses a composition for rollers including: a curing agent having at least two hydrosilyl groups in the molecular chain; a polymer having at least one alkenyl group in the molecular chain and comprising a saturated hydrocarbon unit or an oxyalkylene unit as a repeating unit that constitutes the main chain; a hydrosilylation catalyst; and a foamed elastic layer containing a substance that imparts electric conductivity. However, with respect to the polymer having at least one alkenyl group in the molecular chain and comprising a saturated hydrocarbon unit or an oxyalkylene unit as a repeating unit that constitutes the main chain, a substantially disclosed example is merely use of a polymer having a number average molecular weight of 8,000, and the resulting foam has a hardness, which is determined in terms of ASKER C hardness, to be hardly estimated as being sufficiently soft.
Patent Document 4 discloses a foamable resin composition including: an organic compound having a carbon-carbon double bond and not including a siloxane unit in the molecular skeleton; a compound having SiH having a specific chemical structure; and a compound having an OH group, and a silicone based polymer foam which can be any of from hard to soft obtained from the foamable resin composition. However, the hardness of the soft silicone based polymer is not disclosed, and a suitable formulation for producing a foam having a desired hardness, in particular, as to which polymer having at least one alkenyl group in the molecular chain and comprising a saturated hydrocarbon unit or an oxyalkylene unit as a repeating unit that constitutes the main chain may be specifically used is neither described nor suggested. Although Patent Document 3 discloses a silicone based foamable resin composition, disclosed is to obtain a foam without using a foaming agent.
In addition, as a foam having superior formability and safety, a foamable resin composition including essential components of: a compound having a carbon-carbon double bond; a compound containing at least 1.1 or more Si—H groups per molecule on average; and resin particles containing a foaming agent has been investigated (for example, Patent Document 6).
However, according to this technique, in curing and expanding the foamable resin composition, utilization of the heat generated by an addition reaction between the compound having a carbon-carbon double bond and the compound having Si—H groups makes the basis. Thus, sufficient caloric amount of heat for expansion of the resin particles containing a foaming agent may not be attained in some cases, and a silicone based resin added as a base resin is not expanded; therefore, only a low expansion rate foam of about 5 to 10 times can be achieved, consequently. Moreover, also due to failure in expansion of the base resin, the flexibility and the feel in wearing have been still unsatisfactory.
Under such circumstances, a foam having a high expansion ratio, being superior in flexibility as well as feel in wearing and shock absorbing capacity, and produced without using a material about which toxicity is concerned has been demanded. The reason for such demands is that such a foam can be utilized as a shock absorbing pad for the purpose of preventing occurrence of wounds and impacts against the body during playing sports, and also for the purpose of preventing transcervical fracture in elderly persons.
On the other hand, as elderly population increases in recent years, a concept referred to as “minimization of care needs” to prevent persons from becoming bedridden has been adopted. This is an idea of preventing the state in need of nursing care. As one trigger for lapsing of an elderly person into the state in need of nursing care, bone fracture, particularly transcervical fracture, resulting from falling may be exemplified. Among the bone fracture in elderly persons resulting from falling, particularly the transcervical fracture has been known to account for the basis of the bedridden state (for example, Nonpatent Document 1).
Occurrence of the bone fracture in the vicinity of femur involves two factors, i.e., bone strength and the external force in falling, and the bone strength of young adults beyond the external force in falling decreases to almost half of the external force in falling in the senile stage, which decrease becoming the factor of increase of the bone fracture of the elderly persons (for example, Nonpatent Document 2). It is experimentally ascertained that when the external force beyond the bone strength is applied in falling to the lateral portion of the femoral neck, the femoral fracture is caused at a high rate. Thus, it is suggested that the risk of the bone fracture can be decreased through reduction of the external force that is propagated to the bone when a material for diffusing and absorbing the external force is placed at a greater trochanter part of the femur (for example, Nonpatent Document 3).
Specifically, it was reported that bone fracture of the femoral neck of young adults occurs at 7,200 N, while the strength of the femoral neck of elderly persons has decreased to as low as approximately 2,100 to 3,100 N (for example, Nonpatent Document 4). Since the load applied to the greater trochanter part in falling from standing position is about 5,600 N, bone fracture is inevitable in the range of the bone strengths of elderly persons. Accordingly, it has been accepted that the idea of attaching an external force attenuation device at a greater trochanter part is rational and practically applicable (for example, Nonpatent Document 5).
As similar techniques hitherto, garments provided with a protector at each site for the purpose of preventing occurrence of wounds, and impacts against the body during playing sports have been found. However, such garments to which a protector is directly attached at each site may be suitable for use in sports, but they are not suited as garments for daily use in terms of appearance and comfort in wearing, and the like.
In addition, garments with a shock absorbing pad have been also developed in an attempt to prevent transcervical fracture in elderly persons. Conventional garments with a shock absorbing pad are generally classified into those in which a hard pad is used, and those in which a soft pad is used. The hard pads are of external force-diffusing type, and attenuation of the external force is achieved by elasticity inherent to the material, and also by increasing the area to which the external force is applied (for example, Patent Document 7).
When a hard pad is used, there arise problems of inferior breathability and unpleasant feel in wearing, although the shock absorbing capacity is superior. Although constant wearing is required for sufficiently achieving the effect of preventing the bone fracture, the garments may be taken off intentionally or involuntarily, for example, in bedtime and the like, when an unpleasant feel in wearing is experienced as in the case of hard pads, and falling during such a time period is likely to result in bone fracture.
On the other hand, the soft pad is of external force-absorbing type, and the external force is thermally converted upon deformation of the material, whereby the external force attenuation is achieved. In the case of the soft pads, favorable feel in wearing is enabled, although many of them are inferior in the shock absorbing capacity. Although a polyurethane foam has been predominantly used for soft pads hitherto (for example, Patent Document 8), polyurethane is not adequate for laundering since it has hydrolyzability, and the odor of the remaining reaction catalyst, and the toxicity of unreacted isocyanate are concerned.                Patent Document 1: JP-A No. 2006-131754        Patent Document 2: JP-A No. 2004-358137        Patent Document 3: JP-A No. Hei 8-267612        Patent Document 4: JP-A No. Hei 10-87995        Patent Document 5: JP-A No. 2000-351863        Patent Document 6: JP-A No. Hei 7-196836        Patent Document 7: JP-T (Japanese Translation of PCT International Publication) No. Hei 9-508824        Patent Document 8: JP-A No. 2001-123311        Nonpatent Document 1: Lauritzen J B, Yasushi HAYASHI, Hajime ORIMO: Prevention of bone fracture in falling by hip protector. Osteoporosis Japan, 10: 149-157, 2002.        Nonpatent Document 2: Atsushi HARADA: Prevention of elderly persons from bone fracture in falling. Japan Medical Association Journal, 122: 1955-1959, 1999.        Nonpatent Document 3: Okuizumi H., Harada A., Iwata H., et al: Effect on the femur of a new hip fracture preventive system using dropped-weight impact testing. J Bone Miner Res, 13: 1940-1945; 1998.        Nonpatent Document 4: Cheng X., Lowet G., Boonen S., et al: Assessment of the strength of proximal femur in vitro: Relationship to femoral bone mineral density and femoral geometry., Bone, 20: 213-218; 1997        Nonpatent Document 5: Atsushi HARADA, Hiroyasu OKUIZUMI: Utility of Hip Protector in Bone Fracture in the Vicinity o Femur. Joint Surgery, 23: 1548-1554, 2004.        